The goal of this proposal is to clarify the mechanisms whereby alveolar macrophages contribute to the defense of the lung and to lung injury. The function of alveolar macrophages in the immunological resistance and pathology of the lung is not well understood. We plan to investigate the role of certain macrophage directed lyphocyte mediators, migration inhibitory factor (MIF) and macrophage activating factor (MAF), in the defense functions of the alveolar macrophage. These substances are elaborated by antigen sensitized and stimulated lymphocytes in the course of cellular immune reactions and increase the defense capacities of these cells. The role of certain neutral proteinases associated with the alveolar macrophage which are involved in the pathology of lung disease will also be investigated.